DESCRIPTION: (Adapted From The Applicant's Abstract.) The long-term goal of this research program continues to be a better understanding of adaptation-like effects in the auditory system. Certain recent findings in this lab have drawn attention to a set of issues that go beyond adaptation-like effects, but which can be studied in parallel with them. This lab has previously show that nominally normal-hearing listeners dichotomize on the ability to perform in certain adaptation-like masking tasks in which the relative times of onset of masker and signal are varied. These two populations -- called large and small fringers -- differ systematically on a constellation of other auditory characteristics, including lateral suppression, critical bandwidth, comodulation, overshoot, and the ability to use the cubic distortion product in two-tone masking conditions. This proposal describes a search for additional psychoacoustical tasks on which these two populations dichotomize. In the course of that search, systematic ear and-or sex differences on the various psychoacoustical tasks will also be examined because recent findings from this lab showed correlated ear and sex differences on other important auditory measures. Finding additional correlates with the fringing dichotomy should be helpful to achieving an understanding of these two populations of nominally normal- hearing people, and will be of value to other people studying both normal and pathological hearing. Finding additional ear and/or sex differences in hearing has broad implications both for scientists specializing in hearing and for scientists interested in such topics as brain development, human evolution, cortical lateralization of function, the genetic and prenatal contributions to sex differences in sensory and cognitive functions, etc. This lab has recently shown that spontaneous otoacoustic emissions (SOAEs) are highly heritable, and, from measures obtained from opposite-sex dizygotic twins, they argue that the lesser prevalence of SOAEs in males (and, by inference, their poorer hearing sensitivity) can be attributed to their greater prenatal exposure to androgens. Accordingly, any additional psychoacoustical tasks found to exhibit a sex difference will also be tested on opposite-sex dizygotic, same-sex dizygotic, and monozygotic twins in the search for evidence of both prenatal effects and heritability of these abilities. Knowledge of such heritabilities can guide molecular biological studies of the auditory system. Other experiments will test the recent speculation that the strength of the efferent supply is different to the two ears by measuring tone-evoked otoacoustic emissions and the N1 response, and others will investigate the effects of aspirin, quinine, and exposure to intense sounds on the fringing effect.